Endless waiting status on issuing "Hard Reboot Instance" and "Start Instance" actions from openstack horizon dashboard

Issue

• A VM Instance hangs up. So, we executed "Hard Reboot Instance" in openstack dashboard Action menu.
• But The VM instance endless waiting "Hard rebooting...". So, on another instance we executed "Hard Reboot Instance" which also had same status.
• I restarted nova service of all controller nodes and all compute nodes, but there was no change in the status of the instance.